The efficient removal of low-octane-number straight chain isomers, i.e. normal alkanes, from isomer mixtures is an important step in the generation of mixtures of high octane number for use in gasoline pools as well as for the efficiency of catalytic isomerisation processes. A number of processes have been disclosed dealing with this issue, most of them related entirely to C5/C6 isomer blends. U.S. Pat. No. 4,956,521 discloses the use of different adsorber beds with different specific zeolites for the removal of n-alkanes and mono-branched alkanes from C5/C6 isomers.
U.S. Pat. No. 6,069,289 describes a process for separating multimethylbranched alkanes, which are compounds of high octane number from the effluent of an isomerisation reactor by using a single adsorbent in a moving bed and two desorbents of different desorption capacities. The adsorbent may be silicalite, ferrierite, zeolite Beta, MAPO-31, SAPO-31, SAPO-11, and zeolite X and zeolite Y ion exchanged with cations.
U.S. Pat. No. 6,353,144 describes a process for separating isomers from a C5-C8 isomer mixture by injecting the isomer mixture into a chromatographic separation zone containing a zeolite adsorbent alternately with an eluent that enables the different adsorbed compounds of the isomer mixture to be desorbed.
U.S. Pat. No. 7,037,422 discloses a process for separating the high-octane-number compound naphta from an isomer mixture of C5 and C6 alkanes by contacting the isomer mixture with a CFI zeolite. Branched isomers of C5 and C6 alkanes are adsorbed and subsequently desorbed. In the zeolite, C5 and C6 alkanes are isomerised to the high octane number compounds methylbutane and dimethylbutane, and since methylbutane and dimethylbutane have a lower boiling point than, respectively, the other C5-isomers and C6-isomers, they are recovered by catalytic distillation in the same column.
U.S. Pat. No. 5,210,333 describes the use of adsorption on NaX and NaY zeolites in a fixed bed combined with a hydrogenation functionality that saturates adsorbed aromatics.